In a blog post, the company explained that it still wipes Snapchat messages from its server once they are viewed:

First off, we want to be crystal clear: The Snaps and Chats you send your friends remain as private today as they were before the update. Our Privacy Policy continues to say—as it did before—that those messages “are automatically deleted from our servers once we detect that they have been viewed or have expired.” Of course, a recipient can always screenshot or save your Snaps or Chats. But the important point is that Snapchat is not—and never has been—stockpiling your private Snaps or Chats. And because we continue to delete them from our servers as soon as they’re read, we could not—and do not—share them with advertisers or business partners.

Snapchat claims that its main reason for altering the privacy policy was to make it more understandable. The company did, however, clarify some language about in-app purchases, due to its “Replay” feature, which allows users to see a message even after it expires.